Laser power supply

ABSTRACT

A laser power supply includes a regulator which has a high voltage control loop based on a linear approximation of a laser tube negative resistance characteristic. The regulator has independent control loops for laser current and power supply high voltage.

United States Patent 1191 Bernstein Dec. 23, 1975 LASER POWER SUPPLY[75] Inventor: Daniel Bernstein, Miraleste, Calif.

[22] Filed: Nov. 20, 1974 [21] Appl. No.: 525,592

Primary ExaminerWilliam L. Sikes Attorney, Agent, or FirmJoseph E. Rusz;George Pine [57] ABSTRACT A laser power supply includes a regulatorwhich has a [52] US. Cl 331/945 PE g ltage control loop based on alinear approxima- [51] Int. Cl. H0lS'3/097 on of a la r tube nega iv rei n harac ri i [58] Field of Search 331 /94.5; 330/43; Th regula or h inpendent on rol lo p for l er 328/258, 267 current and power supply highvoltage.

[56] References Cited 2 Claims, 2 Drawing Figures UNITED STATES PATENTS3,541,420 11/1970 Rees 331/945 PE 1c g f VOLTAGE H/Gl/ v04 ms:

0 vs 1 R /A/Pu7 PvWE P C N R E H:

in H/Gh vow:

W wv- J Bot I' -i--wv-y L L/ s C014 Tao L US. Patent Dec. 23, 1975 Sheet1 of2 3,928,819

INPUT US. Patent Dec. 23, 1975 Sheet 2 of2 3,928,819

CONVERTER VOLTFIG E LASER POWER SUPPLY STATEMENT'OF GOVERNMENT INTERESTThe invention described-herein maybe manufactured and used by or for theGovernment for governmental purposes without the payment of any royaltythereon. I I

BACKGROUND or THE INVENTION Current regulation for gas discharge lasertubes is usually accomplished by series ballast resistors or seriescurrent regulators. Unless the. high voltage output of the .laser powersupply tracks the negative resistance characteristic of the tubeg'powersupply efficiency will be lower than need be due to excessive powerdissipation in the current regulator or ballast resistor.

The regulator of the presentinvention has ahigh voltage control loopwhich is based on a linear approximation of the laser tube negativeresistance characteristic. Therefore, for any given tube knowncharacteristics, the selection of one or two resistors will control thehigh voltage, as a function of laser current, such that losses acrossthe current regulating element are minimized. For tubes with welldefined characteristics, the regulator can limit dissipation in thecurrent regulating element from 1 percent to 2 percent of the tubedissipation so that laser power supply efficiencies of 90 percent can beachieved with standard pulse width modulated DC to DC convertertechniques. The regulator has independent control loops for lasercurrent and power supply high voltage.

SUMMARY OF THE INVENTION A laser power supply is provided having aregulator. The regulator has independent control loops for laser tubecurrent and power supply high voltage. A novel feature of the regulatoris simple high voltage and current regulation programmable by the samecontrol signal.

DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawings shows the preferredembodiment of the laser power supply, partly in diagrammatic and partlyin block form.

FIG. 2 shows the details of one form of the voltage converter componentof FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring in detailto FIG. 1, there is shown DC high voltage converter 1 having inputterminals 1a and lb and output terminal 10. Input terminal 2 receivesunregulated input power for application to input terminal la of DC highvoltage converter 1. A series arrangement of preselected resistors R,and R is connected across output terminal and ground to form a voltagedivider network.

Gas discharge laser 3 includes anodes 3a and 3b and cathode 3c. Anode 3ais-connected to output terminal 1c of DC high voltage converter 1. Anode3b receives a high voltage start pulse from terminal 4. Amplifier 10includes inputs 10a and 10b and output 100. Input 10a receives a controlsignal from input terminal 6. Input terminal 10b is connected to groundby way of preselected resistor R,,. Output terminal 100 is connected tobase lla of emitter follower ll. Emitter 1 lb of emitter follower 11 isalso connected to ground by way of preselected resistor R',,. Cathode 3cof gas discharge laser 3 is connected to collector of emitter followerll. Amplifier 20 has two input terminals 20a and 20b and an outputterminal 200. Input terminal'6 is connected to input terminal 20a ofamplifier 20 by way of resistor R Input terminal 201) of amplifier 20 isconnected to ground by resistor R and to fixed reference voltage source5 by way of resistor R Fixed reference voltage source 5 is alsoconnected to input terminal la of DC high voltage converter 1 by way ofresistor R,,. Amplifier 30 includes input terminals 30a and 30b andoutput terminal 300. Input terminal 300 receives a voltage from thevoltage divider network consisting of resistors R, and R Input terminal301) of amplifier 30 is connected to output terminal 200 of amplifier20. The output voltage from amplifier 30 is fed to input terminal 1b ofDC high voltage converter 1.

Now referring to FIG. 2, there is shown one form in which voltageconverter 1 may be configured. This voltage converter 1 is capable ofproviding a regulated output that is reduced from a pre-selected valueas a function of a control input. This can be understood from theequation set out below for the regulated output voltage value when V,. Oand V 0. Voltage converter 1 is shown to include an integrated circuitIC-l constituting a square wave oscillator driving a second integratedcircuit lC-2 configured as a pulse duration modulator. IC-l and IC-2 maybe circuit model NE/SE 555 of Signetics Corporation. The operation ofthese circuits are described in Signetics Corporation ApplicationHandbook at pages 679 and 6-80. a through I: in each integrated circuitIC-l and lC-2 correspond to pin connections numbered 1-8, respectively,in the model NS/SE 555 circuit. The output of IC-2 is controlled as afunction of the error signal received from line lb. The threetransistors 1,, r and 1;, in circuit following IC-2 function as a poweramplifier driving transformer primary T,,. The secondary T, of thetransformer feeds output power to line 1,. via a rectifier-capacitorfilter.

In the operation of the preferred embodiment. DC high voltage converter1 receives unregulated input power from terminal 2 and provides a highvoltage of sufficient amplitude for the operation of gas discharge lasertube 3. Gas discharge laser tube 3 includes anodes 3a, 3b, and cathode30. Gas laser discharge tube 3 also receives at anode 3b a high voltagestart pulse from terminal 4.

The regulator of the power supply has independent control loops forlaser current and power supply high voltage. Amplifier l0 and emitterfollower 1] force the current through resistor R to be equal to V,./R,,,where V, is the laser current control voltage. Amplifier 20 provides acontrol voltage for the high voltage control loop equal to V V,., whereV is a fixed reference voltage provided by reference voltage source 5.Amplifier 30 provides an error voltage which varies the duty cycle ofthe pulse width modulated DC high voltage converter 1 such that the highvoltage is regulated to a value equal to (V V,.) (R, R2)/R when R, R R RIt is noted resistors R, and R comprise a voltage dividing networkpositioned between the output of DC high voltage converter 1 and ground.

A novel feature of the regulator is simple high voltage and currentregulation programmable by the same control signal received at inputterminal 6. If laser current is given by I,, V,-/R,, and high voltage byV,, (V, V,.) (R, R )/R the negative resistance characteristic 3. ofthelaser (decrease in voltage as current is increased) is approximated.Scale factor and slope of the linear approximation is a function of R R-V, and V,..

What is claimed is:

l. A power supply for a gas discharge laser having first and secondanodes and a cathode being comprised of a DC high voltage converter tobe operated in a pulse width modulated mode and having first and secondinput terminals and an output terminal, said first input terminalreceiving unregulated power and providing in response thereto an outputof DC high voltage for application to said first anode of said gasdischarge laser, first and second preselected resistors connected in aseries arrangement from' said output terminal to ground to form avoltage divider network, a first amplifier having an input and outputand receiving at said input a control signal. an emitter follower havinga base. emitter. and collector. said base being connected to said outputof said first amplifier, said collector connected to said cathode ofsaid gas discharge laser. a third preselected resistor connected betweensaid emitter and ground, said first amplifier and emitter followerforcing current through said preselected third resistor so as to beequal to the laser current control voltage divided by the value of saidthird resistor. a fixed reference voltage source, a second amplifierproviding a control voltage equal to the fixed reference voltage appliedthereto minus said laser current control voltage, and a third amplifierreceiving said control voltage and also a preselected voltage from saidvoltage divider network, said third amplifier providing an error voltageto said second input of said DC high voltage converter varying the dutycycle of the pulse width modulated voltage converter such that the highvoltage is regulated to a value equal to the fixed reference voltageminus the laser current control voltage multiplied by the sum of saidpreselected first and second resistors divided by said preselectedsecond resistor.

2. A power supply for a gas discharge laser as defined in claim 1further including means to apply a high voltage start pulse to said gasdischarge laser.

1. A power supply for a gas discharge laser having first and secondanodes and a cathode being comprised of a DC high voltage converter tobe operated in a pulse width modulated mode and having first and secondinput terminals and an output terminal, said first input terminalreceiving unregulated power and providing in response thereto an outputof DC high voltage for application to said first anode of said gasdischarge laser, first and second preselected resistors connected in aseries arrangement from said output terminal to ground to form a voltagedivider network, a first amplifier having an input and output andreceiving at said input a control signal, an emitter follower having abase, emitter, and collector, said base being connected to said outputof said first amplifier, said collector connected to said cathode ofsaid gas discharge laser, a third preselected resistor connected betweensaid emitter and ground, said first amplifier and emitter followerforcing current through said preselected third resistor so as to beequal to the laser current control voltage divided by the value of saidthird resistor, a fixed reference voltage source, a second amplifierproviding a control voltage equal to the fixed reference voltage appliedthereto minus said laser current control voltage, and a third amplifierreceiving said control voltage and also a preselected voltage from saidvoltage divider network, said third amplifier providing an error voltageto said second input of said DC high voltage converter varying the dutycycle of the pulse width modulated voltage converter such that the highvoltage is regulated to a value equal to the fixed reference voltageminus the laser current control voltage multiplied by the sum of saidpreselected first and second resistors divided by said preselectedsecond resistor.
 2. A power supply for a gas discharge laser as definedin claim 1 further including means to apply a high voltage start pulseto said gas discharge laser.